1. Field of the Invention
The present invention relates in general to a video cassette recorder, and more particularly to a circuit and method for maintaining security of a magnetic video tape using a privacy number to prevent others (unauthorized persons) from playing back contents that the user has recorded on the magnetic video tape in a video cassette recorder.
2. Description of the Prior Art
In a video cassette recorder, hereinafter referred to as a VCR, there has been provided an operation of rewinding a magnetic tape toward a first portion of the tape at a high speed when either the playback has been completed up to a last portion of the tape or the playback beginning at the first portion of the magnetic tape is desired by the user.
With reference to FIG. 1, a construction of a conventional video tape is shown. As shown in FIG. 1, the conventional video tape or magnetic tape has first and last portions A and B, respectively, and extending between reels RA and RB. The first and last portions are formed of transparent tape, on which video signals are not recorded. These lead tape portions A and B of the magnetic tape are transparent such that infrared-rays are passed therethrough. The magnetic tape illustrated in FIG. 1 also has a hatched portion corresponding to the portion on which the video signal is recorded.
In FIG. 2, a circuit diagram of a conventional sensing circuit in the VCR is shown. This conventional sensing circuit 100 is provided near the reels RA and RB for winding the magnetic tape, as shown in FIG. 1. As shown in FIG. 2, the sensing circuit 100 comprises an infrared-ray emitting diode IRD which is driven upon being applied with a predetermined power B.sup.+, and supply and take-up sensors 10 and 20, respectively. The supply sensor 10 and take-up sensor 20 each receive an infrared-ray from the infrared-ray emitting diode IRD through the lead tape portions A and B of the magnetic tape.
With the above-mentioned construction, when the VCR initiates its play operation and the lead tape portion A of the magnetic tape approaches near the reel RB, phototransistors Ql and Q2 of the take-up sensor 20 receive the infrared-ray from the infrared-ray emitting diode IRD and apply a desired signal to a microcomputer 30. Upon receiving the desired signal from the take-up sensor 20, i.e., upon perceiving from the take-up sensor 20 that the lead tape portion A has been positioned near the reel RB, the microcomputer 30 controls a deck (not shown) to perform the operation in a rewind mode to rewind the video tape around the reel RA at high speed. When the lead tape portion B is positioned near the reel RA as a result of the above rewind mode operation, phototransistors Q3 and Q4 of the supply sensor 10 receive the infrared-ray from the infrared-ray emitting diode IRD and apply a desired signal to the microcomputer 30. Upon receiving the desired signal from the supply sensor 10, the microcomputer 30 recognizes that the lead tape portion B has been positioned near the reel RA and controls the deck to complete the rewind mode operation.
At this time, if the operation of the VCR is initiated from the position of the magnetic tape where the infrared-ray from the infrared-ray emitting diode IRD is transmitted through the lead tape portion B, the microcomputer 30 performs an eject operation in response to the sensed signal from the supply sensor 10. That is, the VCR cannot perform the operation in either a play mode or a fast-forward mode.
For this reason, the microcomputer 30, upon sensing that the lead tape portion B has been positioned near the reel RA as a result of the rewind mode operation, completes the operation in the rewind mode. Then, the microcomputer 30 changes the mode of operation from the rewind mode to the fast-forward mode to wind the video tape around the reel RB by a predetermined number of times, so that the lead tape portion B is not exposed to the infrared-ray emitting diode IRD.
However, the conventional VCR has a disadvantage, in that, everyone having access to the video tape can play back video and audio signals recorded on the video tape. Therefore, everyone is capable of playing back even the contents on the video tape held restricted by the user. As a result, for the purpose of maintaining security of the contents of the video tape, the video tape must be kept in an inaccessible place, creating an inconvenience.